1. Field of the Invention
This invention relates to a wireless power receiver, and more particularly to a rectifying-and-modulating circuit and a wireless power receiver incorporating the same.
2. Description of the Related Art
Referring to FIG. 1, a conventional wireless power receiver can cooperate with a wireless power transmitter (not shown) to achieve power transfer and data communication. The conventional wireless power receiver includes a power receiving circuit 11, a full-bridge rectifier 12, a filtering capacitor 13, a modulating unit 14, two switches 15, and two modulating capacitors 16. The power receiving circuit 11 is used to wirelessly receive power transmitted from the wireless power transmitter so as to generate an induced current. The induced current generated by the power receiving circuit 11 is rectified by the full-bridge rectifier 12 and then, is filtered by the filtering capacitor 13. The modulating unit 14 is operable to control operation of each of the switches 15 between conduction and non-conduction based on communication data, thereby changing an amplitude of the induced current generated by the power receiving circuit 11 and thus changing an amplitude of an output current, which is generated by the wireless power transmitter for wirelessly transmitting the power to the conventional wireless power receiver. As a result, the wireless power transmitter can determine the communication data based on the change in the amplitude of the output current.
It is noted that the full-bridge rectifier 12, the modulating unit 14 and the switches 15 are generally integrated into an integrated circuit. Thus, the modulating capacitors 16 required to modulate the induced current generated by the power receiving circuit 11 are external to the integrated circuit, and occupy a relatively large area. In this case, the conventional wireless power receiver has a relatively high cost and occupies a relatively large area.
Moreover, since the full-bridge rectifier 12 is constituted by four diodes 121, the conventional wireless power receiver may have decreased power conversion efficiency. Referring to FIG. 2, in order to solve this problem, four N-channel metal oxide semiconductor field effect transistors (NMOSFETs) 122 are used to replace the diodes 121 of FIG. 1, and an additional rectifier control unit 17 is used to control operation of each of the NMOSFETs 122 between conduction and non-conduction. Upon start-up or light load operation of the conventional wireless power receiver, the rectifier control unit 17 is operable to control the NMOSFETs 122 to be non-conducting such that the induced current generated by the power receiving circuit 11 is rectified by parasitic diodes each formed between a bulk and a drain of a respective one of the NMOSFETs 122. Otherwise, each of the NMOSFETs 122 is controlled by the rectifier control unit 17 to alternately change between conduction and non-conduction so as to rectify the induced current generated by the power receiving circuit 11.